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Characterization of Inclined Jet in Cross Flow for Thin Film Cooling via Large Eddy Simulation

Investigates inclined jet in cross flow via LES, focusing on thin film cooling for turbines. Analyzes vorticity fields and coherent structures.

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Characterization of Inclined Jet in Cross Flow for Thin Film Cooling via Large Eddy Simulation

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  1. Flow Characterization of Inclined Jet in Cross Flow for Thin Film Cooling via Large Eddy Simulation I.Z. Naqavi1, E. Savory1 & R.J. Martinuzzi2 1Advanced Fluid Mechanics Research Group Department of Mechanical and Materials Engineering The University of Western Ontario 2Mechanical and Manufacturing Engineering University of Calgary

  2. Overview: • Jets in Cross Flow • Thin Film Cooling • Background • Current Work • Large Eddy Simulation • Results • Conclusions

  3. Jets in Cross Flow: • A flow configuration representing a variety of industrial and environmental flows. • A jet is introduced from the wall at a certain angle to the main stream. • Used in VTOL, thin film cooling, pollutant dispersion etc.

  4. Thin Film Cooling: Hot fluid Cooling film Cold fluid Holes for film cooling on turbine blade. Thin film cooling (Durbin, 2000) • Separation of a hot fluid from a wall by a cold fluid, in form of a thin layer ejecting from wall, is called thin film cooling.

  5. Background: Counter rotating vortex pair Jet shear-layer vortices Horseshoe vortices Wake vortices Wall • Four major structures have been identified i.e. horse shoe vortex, jet shear-layer vortex, counter rotating vortex pair and wake vortices.

  6. Current Work: • In this work LES is performed for inclined jet in cross flow. • Effort is being made to introduce a cross flow with true turbulence. • Previous LES simulations lack effective turbulence specification at the inlet. In this work a real turbulent field is specified at the inlet. • This will enhance the understanding of the effect of background turbulence on the jet in cross flow.

  7. Large Eddy Simulation: • In LES spatially filtered unsteady Navier Stokes equation are solved numerically.

  8. Large Eddy Simulation (cont.): • A fractional step scheme (Moin, 1982) is used to solve Navier Stokes equations. • A semi implicit time advancement scheme is used where convection terms are discretized explicitly with 3rd order Runge-Kutta scheme and diffusion terms are discretized implicitly with Crank-Nicolson scheme. • Resulting set of linear system is approximately factorized and solved using Tri-diagonal matrix algorithm. • To solve pressure poisson equation fourier decomposition is applied in span-wise direction and resulting system of equation is solved using cyclic reduction method.

  9. Large Eddy Simulation (cont.): • ReD =3500 • Domain size • Grid size • At inlet a true turbulent velocity field is specified for that purpose a separate channel flow code is run and velocities are saved at a plane for some 150 flow through time.

  10. Results

  11. Average Vorticity Field: Average stream-wise vorticity at different y-z planes

  12. Streamlines overlaid on average stream-wise vorticity on a y-z plane at x=5D showing counter rotating vortex pair.

  13. Average wall normal vorticity at the bottom x-z plane Average span-wise vorticity at the central x-y plane

  14. Instantaneous Vorticity Field: Instantneous stream-wise vorticity at different y-z planes

  15. Instantaneous wall normal vorticity at the bottom x-z plane

  16. Instantaneous span-wise vorticity at the central x-y plane

  17. Coherent Structure: • Coherent structures can be represented by iso-surfaces of pressure poisson.

  18. Coherent structures for inclined jet in cross flow (Laminar)

  19. Hairpin structures Stream-wise structure Coherent structures for inclined jet in cross flow (Turbulent)

  20. Conclusions: • Instantaneous flow picture is presenting a very strong interaction of cross flow with jet. • Vortical structures coming from upstream interact with the jet. • Such interactions can have strong influence on heat transfer. http://www.eng.uwo.ca/research/afm/default.htm

  21. Thank you

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